The invention is directed to a method for the preparation of highly elastic foams of reduced compression hardness having urethane groups by the reaction of polyethers having a molecular weight of 400 to 10,000 and containing at least two hydroxyl groups with polyisocyanates in the presence of cross-linking agents, catalysts and water and optionally in the presence of emulsifiers, stabilizers, organic blowing agents and further auxiliaries and additives.
Flexible polyurethane foams are used to a large extent in upholstered furniture and automobile industries. For the different uses and the different qualities desired therefor, it is necessary to be able to vary the apparent density and primarily also the compression hardness over a wide range.
Inorganic and organic fillers have already been used for preparing foams with increased compression hardness. The compression hardness can also be increased by polymerization reactions of the polyols used for foaming.
Compression hardness is lowered by the use of physical blowing agents, such as fluorocarbons or methylene chloride. The use of these materials is contrary to the endeavor, for environmental reasons, to limit the use of fluorocarbons as much as possible. The same is true for methylene chloride, which is physiologically not safe.
In formulations in which inert fillers are used in order to obtain other foam properties instead of an increase in hardness, according to the state of the art, the use of physical blowing agents is even indispensable when flexible foams are to be obtained. For example, considerable amounts of melamine or aluminum hydroxide are used in order to manufacture upholstered furniture and mattresses of high flame resistance on the basis of highly elastic, so-called HR foams. The increase in compression hardness, which is associated therewith, cannot be accepted for reasons of comfort, so that physical blowing agents must be used in considerable amounts.
The addition of compounds which contain at least one polyoxyalkylene group and at least one anionic group to formulations for the production of polyurethane foams is known from the art.
For example, the use of a mixture of polyoxyalkylene alkyl ether sulfate and a polyoxyethylene/polyoxypropylene polymer as emulsifier and dispersing agent for the manufacture of flexible polyester urethane foams is described in CS patent 253,786.
The use of anionic surfactants as foam stabilizers for the preparation of flexible polyester polyurethane foams is known from the German Offenlegungsschrift 11 78 595.
The use of nonylphenol polyoxyethylene ether sulfates as foam stabilizers for the preparation of rigid polyurethane or polyisocyanurate foams can be inferred from U.S. Pat. No. 4,751,251.
Japanese patent 56/152 826 discloses the use of carboxymethylated polyether polyols as trimerizing catalysts for the preparation of rigid polyisocyanurate foams. Derivatives of aminated, alkoxylated aliphatic alcohols with sulfonate or carboxylate groups as trimerization catalysts for forming rigid polyisocyanurate foams is disclosed in the U.S. Pat. No. 4,235,811.
However, the use of such anionic surfactants for the preparation of highly elastic, so-called high resilient polyurethane foams cannot be inferred from the state of the art; nor is the use known of such surfactants for the preparation of polyurethane foams of reduced compression hardness.